Ohh...
Tuna fish sandwiches take 15 minutes to prepare.
Just take some canned tuna, dump it in a bowl, mix some mayonnaise, mustard, diced celery and tomatoes and some salt and pepper to taste and your good.
Among the above, I also like raisins, crushed walnuts, paprika, a little cayenne pepper, lemon juice, and a little soy sauce and ginger, and finally wasabi.
Yeah I know, a little complex, but it is worth it if you have the ingredients around (wasabi comes in handy for many recipes, plus a little bit goes a long, so I suggest getting a tube for $4).